Extracts of bovine brain catalyze the degradation of enkephalins. Fractionation of these extracts on DEAE-cellulose columns resolves this activity into two protein components both of which are required for maximal activity. The first component has been purified over 400 fold and shown to catalyze the cleavage of the tyrosyl-glycine bone of methionine enkephalin. This preparation also catalyzes the hydrolysis of a number of phenylalanine containing depeptides of the type X-phenylalanine, but has been shown to be distinct from leucine aminopeptidase. The dipeptidase activity of this preparation has been shown to be identical to the enkephalin peptidase activity by zymogen stains on disc gel electrophoresis. The affinity of this enzyme for enkephalin is almost an order of magnitude lower than that reported for an arylamidase from monkey brain, and the dipeptidase activity differentiates this activity from the previously described arylamidase of bovine brain. These results suggest an unique protein may be involved in the degradation of enkephalins.